Flow control mechanisms which are adjustable to provide a proportionally variable rate of fluid flow in response to changes in fluid pressure heretofore have utilized a piston disposed within a chamber. The piston is movable within the chamber and is biased by a spring toward the inlet of the chamber. Pressurized fluid introduced through the inlet port in the chamber acts against the biasing force of the spring to move the piston axially within the chamber. The extent of axial movement within the chamber is dependent upon the fluid pressure acting against the piston at the inlet of the chamber. Fluid exits from the chamber through a plurality of outlet ports, with the rate of flow through the outlet ports being regulated by the extent to which the piston blocks the outlet ports. Accordingly, axial movement of the piston within the chamber constitutes a shutter mechanism that varies the degree of openness of the outlet ports in response to the fluid pressure at the inlet of the chamber. Typical is the regulator shown in U.S. Pat. No. 2,984,261.
In valve mechanisms of the type described, the flow of fluid introduced into the chamber through the inlet generally passes through an opening that extends through the interior of the piston to the outlet ports. Accordingly, it has been the case that leakage between the piston and chamber wall has been sought to be eliminated. Either a diaphragm arrangement or a piston-cylinder combination having very close tolerances is required to prevent flow around the outside of the piston. However, the use of sealing mechanisms between the piston and chamber wall restricts axial movement of the piston and reduces the responsiveness of the valve mechanism to slight variations in pressure.
To overcome the leakage by machining the piston to an outside diameter and the chamber wall to an inside diameter of close tolerances as a practical matter, is cost prohibitive.
Another approach taken in an attempt to solve the leakage problem is that of utilizing a resilient diaphragm disposed between the piston and the chamber wall wherein the flow of fluid is directed by the diaphragm from the inlet of the chamber to the interior of the piston. Erickson, U.S. Pat. No. 3,422,842, discloses such a valve mechanism wherein a diaphragm is secured between the movable piston and the chamber wall. The diaphragm prevents the flow of fluid from the inlet around the exterior of the piston.
Valve mechanisms that regulate the flow of fluid therethrough in response to the pressure of the fluid have many applications. However, the present invention is particularly suitable for employment in apparatus that dispense carbonated beverages, particularly where such beverages are mixed in situ from carbonated water and a syrup.
The source of pressurized fluid for input into the valves described above is generally controlled by a direct mechanical connection. This type of connection generally does not provide the rapid on/off response and reliability required in a system for dispensing beverages.